1. Field of the Invention
This invention relates generally to concrete panels for use in making concrete decks or floors for spanning between structural supports; and more particularly to resilient grout seals for precast concrete panels and beams used in constructing reinforced concrete decks for bridges supported by structural beams, and methods for fabricating concrete panels, decks, and support beams having grout seals.
2. Brief Description of the Prior Art
The construction of reinforced concrete decks and floors (e.g. on bridges and in buildings) has always been the most labor intensive and most costly component of the superstructure involved, and has been the component that controls the overall rate of progress of the construction. The need for temporary support of the reinforcing steel and freshly poured concrete until the concrete has attained sufficient strength to support itself is a major factor in the cost of such construction. The length of time such support must remain in place to allow the concrete to attain sufficient strength is the major factor in controlling the rate of progress of the structure.
The original method to provide the temporary support was to use a basic wood form made up of boards or plywood sheeting nailed to wood joist members, carried on wood timbers or steel beams, which in turn were supported on posts or columns from the ground or lower completed floor. This method is still used today with the development of a variety of complex high capacity column scaffolding systems and beam members that are adjustable for both span length and camber. Other developments in the use of the basic wood form include hanger systems that provide for hanging the form from the beam members of the permanent structure, thereby eliminating the need of posts or columns from below. Another development involved trussed framing systems that provided for the support of large areas of form on a very few bearing supports, and for the removal and re-setting of such large areas as a single unit.
The cost of using basic wood forms would be prohibitive if they were used just once, but they are normally not consumed or destroyed in a single use and are in fact in normal practice re-used several times before wear and tear makes them unfit for further re-use. The greater the number of re-uses of the forms, the more economical they become. Economics therefore dictates that the effort on any given project is to provide the minimum quantity of form that will permit reasonable progress to be achieved on the project, thereby gaining the greatest number of re-uses, even though availability of a greater quantity of forms would provide for a faster rate of progress.
The setting of wood forms preparatory to the placement of reinforcing steel and concrete is a labor intensive task by itself, but removing wood forms after the concrete has attained sufficient strength, usually requiring extensive scaffolding, requires a greater amount of costly labor and equipment. Moving to the location of its next use and the clean up and preparation for re-use of the form adds more labor and equipment cost.
The high labor and equipment costs, and the limitation of progress inherent in the use of wood forms, has encouraged development of alternative methods of providing support for deck and floor construction. The development of methods using materials that are durable, yet economical enough to be used once and then left in place, are gaining in favor. Some methods provide temporary support only and after the concrete has gained its strength are simply left in place. Light gage galvanized corrugated sheet steel panels supported directly by the permanent structure beams id the most popular of these methods.
Some methods provide temporary support but in addition become an integral permanent working part of the structure when the concrete gains its strength. Heavy gage corrugated sheet steel panels, supported directly by the permanent structure beams, with loop shear connectors connected (e.g. by welding) to the panels and then embedded in the concrete to make the panels and the cured concrete work as a composite unit is one example of this method. The most recent development in this area is the precast pre-stressed concrete panel supported directly by the permanent structure beams, and again the panels and the cast-in-place concrete work as a composite unit. The panels replace the wood forms and serve both as a form and as an integral part of the structure. A desired amount of concrete is poured onto the already-formed and already-hardened panel.
In becoming a permanent composite component of the structure, the panels replace structural materials that would otherwise have to be provided in the design of the structure. In the case of the sheet steel panels, part of the reinforcing steel is replaced by the panel. In the case of the pre-stressed panel, a substantial part of the reinforcing steel and of the concrete is replaced by the panel.
In exposed structures such as bridges, the concrete panels are popular with engineers and architects because they blend in with the appearance of the structure and provide the most natural look. Another important reason is that they are not subject to corrosion that might diminish the appearance at some later date, or even become a hazard by falling from the structure as sheet steel might do.
The currently popular design of pre-stressed concrete panels leaves serious and costly problems in the construction technique. To accomplish the composite relationship between the panel and the cast-in-place concrete, the first requirement is that the panel have a continuous rigid bearing contact with the top of the supporting beam along its ends. Since neither the top of the beam or the bottom of the panel can be depended upon to be perfectly flat, an intervening material, normally concrete or cement grout, that can be installed in a plastic state so it will conform to both surfaces and then harden in that shape is required. General practice (see FIG. 1) is to place a narrow strip of fiberboard along the edges of the top flange of the supporting beam, to set the concrete panel thereon so the panel overhangs the fiberboard strip over the beam, and then to either force the intervening material in its plastic state under the overhanging part of the panel, or wait until the cast-in-place concrete is poured and at that time force the concrete mix being used to flow under the overhanging part of the panel. The fiberboard is of sufficient thickness to allow for the intervening material to be forced under the overhanging part of the panel, and it prevents the plastic material from flowing over the edge of the beam.
To provide for the deflection of the beams and the design cambers that are required to provide the desired finished grade, the designer and/or the constructor is left with three undesirable options in the use of this method. The thickness of the fiberboard material (or other filler or sealing material) can be varied to compensate for deflection and camber which allows the thickness of the slab to remain constant; the thickness of the slab can be varied to provide the desired top surface grade while the bottom surface follows the deflection and camber of the beam; or the top surface of the beam can be re-graded to provide for deflection and camber with a cast-in-place concrete overlay prior to the placement of the fiberboard strips.
If the thickness of the fiberboard strip is varied, (see FIG. 1) measurement and placement of the strips according to a pre-calculated layout must be done by workmen working on top of the bare beams before the panels can be placed. This is slow and dangerous work, and completed work can easily be knocked or blown off of the beam, and at best the amount of variation that can be accomplished is very limited because excessive thickness of the fiberboard becomes unstable.
Methods of using concrete bricks under the panels along with galvanized sheet steel angles (see FIG. 3) to close the opening between the panel and the top of the beam between bricks are available, but extremely labor intensive and time consuming. There is no way to adjust panels after they are in place, so if errors are discovered at this time, the only way to make corrections is to remove the panels and start over.
If the thickness of the slab is varied, all the variation must be in added thickness, since design requirements are a minimum thickness. The cost of the excess concrete is a complete loss and again the amount of variation that can be accomplished is very limited because too much excess concrete would add too much dead load to the slab and to the structure.
Re-grading the top surface of the beam (see FIG. 2) provides satisfactory results, but is clearly the most costly and time consuming of all of the options.
The most recent method to provide the variable space between the bottom of the panel and the top of the beam and to prevent the plastic material from flowing over the edge of the beam is the use of threaded bolts inserted through threaded inserts embedded in the panels when cast, to support the panel, and a plastic seal strip, also embedded in the panel when cast, and installed on the structural beams with the use of a special erection tool, to prevent the plastic material from flowing over the edge of the beam (see FIG. 4). In this method typically four threaded inserts are embedded in each panel, two along each end of the panel that will overhang the structural beam when the panel is erected in place and near the quarter points along the length of the panel. A plastic seal strip is positioned horizontally on the bottom of the panel with one edge embedded in the panel the full length of each end of the panel that will overhang the structural beam. The embedded edge is positioned to fall over the edge of the structural beam when erected and the other edge extends a short distance beyond the end of the panel. Either in the casting yard, or when the panels are delivered to the structure on which they are to be used, threaded jack bolts are inserted through the four embedded threaded inserts to extend a desired distance below the bottom of the panel. The jack bolts move the seal strip as they protrude from the bottom of the panel, and a special seal depressor erection tong (see FIG. 8) moves the strip to rotate about the embedded edge past the vertical to a position for them to pass down between the two supporting beams as the panel is lowered into position on the bridge. The erection tong provides attachment to the panel for it to be lifted and set in place on the support beams. When the panel is set in place it bears on the threaded jack bolts and the seal depressor erection tong is released allowing the seal strips to spring back to contact the top edges of the beams to accomplish the grout seal. The panel can then be graded by use of the jack bolts while the seal strip maintains its seal by sliding up or down on the edge of the beams.
This method provides for a constant thickness slab with a wide range of adjustability for camber and deflection but still leaves serious and costly problems. The successful use of the plastic in the seal strip depends on the distribution of unit bending over a wide band of the strip to avoid stress concentration, however the prior art is subject to grout intrusion that forces localized bending and thereby stress concentration. In the application where the seal strip is left in its erected and therefore stressed state for an extended period of time, stress relaxation and deformation reduce the pressure against the side of the support beam and its ability to effectively seal the grout. The seal depressor erection tong is an expensive extra piece of equipment. Due to rotation of the tines around the ends of the panels, interference with reinforcing steel protruding from the top of concrete support beams, or shear studs welded to the top of steel support beams is frequently encountered and costly adjustments in the reinforcing steel or studs is necessary.
Bridge designers are constantly increasing the length of bridge spans and thereby increasing camber and deflection so the wide range of adjustability of this method is sometimes still not enough. Two methods to increase the range of adjustability of the present method are to make the seal strip wider, and make it out of a stiffer premium material capable of withstanding the degree of bending and rebound required, or making the seal strip thicker to make it stiffer, which would also require a premium material due to the substantially higher stresses developed in the thicker material bending to the required radius. The premium material is inherently expensive and the extra width required for the increased haunch height adjustability would have to protrude out from under the edge of the panel in the casting bed, where it would be an obstacle to the bulkhead form. The protruding seal strip would also be subject to damage during storage and handling of the panel and require excessive blocking or dunnage between panels to allow for the swing of the strip when deflected for erection by the erection tool.
There is also a problem with the threaded jack bolt in that, when they are inserted through the embedded threaded insert and they deflect the seal strip, the sharp bottom edge of the bolt sometimes cuts into and tears the seal strip. If the bolt bottom edge is chambered or filleted, the reduced bearing area of the bolt on the structural support beam can become insufficient and scouring and deformation can occur.
Thus, there is a need for efficient and economical apparatus and method for making a concrete deck to span structural supports that is quick to set, and free of problems due to casting yard grout intrusion, and capable of remaining effective for extended periods between panel erection and pouring of cast-in-place concrete. There also is a need for efficient and economical apparatus and method for making a concrete deck to span structural supports that is quick to set, and that is easy to grade on the ever increasing span lengths, with their ever increasing span lengths, of current and future bridges. There is further a need for an efficient and economical apparatus and method for making a concrete deck to span structural supports that is quick to set without special tools or equipment, or interference with beam reinforcing steel or studs when the bridge design requires it. There also is a need for an attachable foot for the threaded jack bolt that will both reinforce the bearing of the bolt on the structural beam and prevent the bolt from cutting and tearing the seal strip during erection.
There are several patents which disclose various apparatus and methods for constructing concrete beams, panels and decks.
My previous patents, Horstketter, U.S. Pat. Nos. 4,982,538 and 5,218,795 disclose concrete panels, concrete decks, parts thereof, and apparatus and methods for their fabrication and use.
O""Keefe et al, U.S. Pat. No. 4,761,927 discloses a pair of finger gaskets that extend between opposed laterally spaced sides of a pair of C-shaped rafters in overlapped relation and which slide over each other.
None of these references taken alone or in any combination teaches or suggests a flexible resilient grout seal strip with a support beam/precast concrete panel connection in accordance with the present invention.
The present invention is directed to apparatus and methods which solve the problems of the prior art and provide the means to set precast reinforced, or precast pre-stressed concrete panels that span between beams directly on the supporting structural beams with no prior preparation; to adjust the grade of the panels to provide for deflection and camber over a wider range of adjustment than provided by the prior art, before or after setting, with little or no loss of material. The present apparatus and methods do not require the use of a special seal depressor tool in situations where interference with reinforcing steel protruding from the top of concrete support beams, or shear studs welded to the top of steel support beams, would otherwise occur with the use of such tool. Another aspect of the present invention overcomes the problems of the prior art and provides the means to avoid tearing the seal strip when inserting threaded jack bolts and to reinforce the bearing of the jack bolts.
In the precast deck panels of this invention, threaded jack bolts may be used to provide adjustability of each panel. The seal that contains the grout or concrete that is forced between the bottom of the panel and the top of the supporting beam for bearing slides on the edge of the beam, or on the bottom surface of the panel, and is capable of maintaining its sealing action over a wide range of adjustment of the space between the two. At any stage prior to pouring concrete on a panel, the bolt can be adjusted upwardly (or downwardly) and the grout seal will extend sufficiently that the seal between the beam and the panel will be maintained. The grout seal also acts as a concrete form and is capable of resisting the horizontal pressure of the plastic grout or concrete poured against it and thereby prevents it from simply flowing over the edge of the beam.
The present grout seal strip deflects to the position to pass down between the support beams for erection with less unit bending and stress than the prior art. The reduced unit bending and stress during the erection procedure provides an increased rebound pressure against the side of the support beam and an increased resistance to the horizontal pressure of the plastic grout or concrete poured against it. In the prior art, an open inverted xe2x80x9cVxe2x80x9d at the anchor is intended to provide room for the seal strip to deflect so the deflection will start at the anchor edge of the strip and attain unit deflection over a wide band of the strip, thus minimizing the unit deflection and stress at any point during the deflection required by the erection procedure. However, during the casting of the panel, grout from the panel seeps into and fills the space provided, forcing the seal strip to concentrate deflection over the hardened grout and developing high concentrated stress at that point. The present invention solves this problem by providing a wide convex cavity with a long radius bend forming one side and a relatively flat sloping opposite side at the anchor so that any grout that seeps into it and hardens will be easily expelled by the deflection of the strip. The long radius bend is thickest at the anchor, and tapers down over a wide portion of the strip to improve the distribution of unit deflection and further minimize unit stress at any point.
For situations where the panels are in place for an extended period of time between their erection and the pouring of the cast-in-place concrete, such as erection of the panel during the winter and the pouring of the cast-in-place concrete in the spring, the present invention provides a seal strip having a wide flat portion with an inverted anchor channel portion along one longitudinal side that embeds into the bottom of the panel and has a vertical angularly sloped leg portion integrally hinged to a horizontal top portion. When the seal strip is deflected by the erection tong, its flat portion and sloped leg portion rotate as a unit about the hinge with little bending and stress. At a predetermined point in the rotation of the seal strip, its wide flat portion will contact the opposite generally vertical leg of the channel at the bottom of the panel, and/or the rotated sloped leg will bear against the top of the inverted channel, and then bend the remaining wide flat portion. To keep grout from filling the channel during the casting of the panel, it is filled with a plastic foam or like material. If a closed cell foam material is used, the air trapped within the closed cells will compress and react about the hinge to provide added load to force the seal strip against the side of the supporting beam and the compressed air will act as a spring that will compensate for any stress relaxation and deformation in the plastic.
For bridges designed with extreme haunch heights, the present invention provides a two-part seal made up of an anchor channel embedded in the panel and a seal strip that is inserted into the anchor channel. The anchor channel is positioned on a line that will fall approximately over the edge of the supporting beam when the panel is erected and in the erection procedure, the seal strip will bear against the side of the top flange of the supporting beam for the full length of the panel.
The grout seal strips and anchor channels can embedded in the bottom of the concrete panels during the casting of the panels, and after the panel is cured and removed from the forms the embedded anchor can either be left in place, or removed to form an anchor channel in the concrete, to receive and secure the seal strip portion.
Due to the necessary increase in the stiffness of the seal strip with increased space between the bottom of the panel and the top of the supporting beams, the panel adjustability of the prior art is limited. As the space increases, so does the length of seal subject to the horizontal pressure of the grout or concrete poured against it, and because the seal acts as a cantilever beam, the stress in the seal is compounded by greater load and increased span. The adjustability of the prior art panels is limited by the capacity of a thicker or stiffer plastic material to deflect from the horizontal as-cast position through the 135 degree bend to the position preparatory to passing down between support beams in the erection procedure, and still rebound to apply sufficient pressure against the side of the top flange of the support beam to resist the horizontal pressure of the plastic grout or concrete poured against it and provide an adequate seal. The panel adjustability of the prior art is also limited by the practical limit of the width of the seal strip that can be accommodated by the bulkhead form in the casting bed.
The seal strip of the present invention can be made in a variety of widths and stiffness to provide for greater panel adjustment because by being inserted into the embedded or formed anchor channel after the panel is removed from the form, it can be shaped to require less deflection, or no deflection at all to the position preparatory to passing down between support beams in the erection procedure. The lower erection stress provides greater rebound at any space between the panel and the support beam and thereby a better seal against leakage of grout.
For bridges designed with reinforcing steel protruding from the top of concrete beams, or shear studs welded to the top of steel beams, that would interfere with the operation of the erection tong, the present invention provides a grout seal strip having an anchor portion of which can be embedded into the top of the beam in the casting bed, rather than the panel, or secured to the top edge of the beam at any time prior to the setting of the precast panel. The grout seal strip can be positioned to stand near vertical along the edges of the top flange of the beam for the full length of the beam with the top edge of the strip curved or bent to the outside so it will deflect to the outside under the weight of the panel being lowered down on it. When used with structural steel beams, the strip may be bonded to the top edge or side of the top flange, or may be molded with a pair of horizontal extensions that fit under and over the flange plate in a tight fit, or be secured with straps from the strip on one edge across the beam to the strip on the opposite edge at spaced intervals along the beam.
When conventional jack bolts of the prior art are inserted through the embedded threaded inserts, they first encounter and deflect the seal strip. Due to the sharp square edge of the bottom of the bolt, puncture and tearing of the seal strip can occur. When the jack bolt is used in a maximum size panel, and is set to bear on a rough surface support beam, the bottom end of the bolt can be abraded away as the bolt is turned to raise the panel. The present invention solves those problems by providing a foot that is easily attachable to the bottom of the jack bolt.
It is, therefor, an object of the present invention to provide a novel, efficient, and economical apparatus and method for forming concrete decks or floors between structural supports.
Another object of the present invention is the provision of a precast concrete panel which can span between structural supports and can rest directly on the supports.
Another object of present invention is the provision of such panels with means for adjusting the grade of the panels to provide for deflection and camber before or after setting with little loss of material.
Another object of the present invention is the provision of a grout seal for such panels that ejects any grout that may seep into and harden in the anchor void.
Another object of the present invention is the provision of a grout seal for such panels that employs compressed air to provide spring sealing pressure, and compensates for plastic stress relaxation and deformation.
Another object of the present invention is the provision of a grout seal for such panels that requires no special tools or equipment to erect the panels.
Another object of the present invention is the provision of a grout seal that requires no panel end clearance for an erection tool.
Another object of the present invention is the provision of a grout seal strip with a separate anchor for embodiment in a precast concrete panel.
Yet another object of the present invention is the provision of a grout seal strip with means for attachment to the bottom of a precast concrete panel after fabrication of the panel.
A further object of this invention is the provision of a foot to be used in conjunction with the jack bolt of the prior art that will prevent the bolt from punching and tearing the seal strip.
A still further object of this invention is the provision of a foot to be used in conjunction with the jack bolt of the prior art that will protect the bolt against abrasion.
To those of skill in this art who have the benefit of this inventor""s teachings, other and further features, objects, and advantages will be clear from the following description of the preferred embodiments where taken in conjunction with the drawings, and of which are given for the purpose of disclosure.